Gelatin/polyvinyl alcohol films incorporated with different blueberry extracts as potential colorimetric indicators to detect acidic and basic vapors

Abstract

Blueberry extract is rich in phenolic compounds and anthocyanins, which can undergo color changes when subjected to different pH conditions. This feature makes it liable to be incorporated into polymeric matrices to form colorimetric indicator films. In this sense, films based on gelatin and polyvinyl alcohol (PVA) were elaborated with raw blueberry extracts (EB), purified fractions of phenolic extract (EF), or anthocyanin extract (EFA). Their color sensitivity to acidic and basic vapors was investigated. Higher levels of phenolic compounds and total anthocyanins were observed for EB and EFA. The EFA was more sensitive to acidic and basic vapors, with an intense visual colorimetric change attributed to the anthocyanins. The higher absorbance in the 400 nm wavelength region observed in both EF and EB spectra was possibly due to the presence of yellow phenolic compounds. Corroborating to the findings for the extract, the EFA film presented a tone shift over time and a higher overall color difference, completely changing from a greenish color to purple under acidic vapors. However, the EB film has shown to be more susceptible to basic conditions, exhibiting differences in h° values over time under basic vapors. Therefore, PVA/gelatin films incorporated with EB are recommended for the colorimetric indication of nitrogenous bases, and the EFA-added films for volatile acids. Based on the results, films incorporated with EB or EFA can be used to monitor, detect, and report the presence of acidic and basic volatiles from food deterioration.